[BUGFIX] Loose return value in HtmlentitiesDecodeViewHelper

The return value of HtmlentitiesDecodeViewHelper can be null
e.g. {foo -> f:format.htmlentitiesDecode()}
with foo might be undefined

Resolves: #102553
Releases: main, 12.4
Change-Id: I41fa1917f23a40a742e1ebc27ef37d6fee0bd858
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82033


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>